1. Field of the Invention
The present invention relates to a chain hoist position encoder assembly which may be removably attached externally on the casing of a chain hoist to track the movement of the load carried by the chain hoist relative to a fixed location.
2. Description of the Prior Art
Chain hoists are utilized in many different applications to raise and lower loads suspending from overhead supports. A chain hoist is comprised of a heavy-duty motor housed within a rugged casing and having at least one chain access opening in the casing. A chain may be suspended from an overhead support or from the chain hoist itself to carry a load. In either case the chain is routed around a chain drive gear located within the chain hoist casing. The chain drive gear within the casing is driven by the chair hoist motor. The slack portion of the chain, after passing around the drive gear within the casing, is routed back out through the chain opening and hangs from the chain hoist casing as a slack end having a length that varies with the position of the chain hoist casing relative to the overhead support or with the position of the load relative to the chain hoist casing.
The chain hoist motor, through the internal chain drive gear within the casing, pulls either the load or the motor casing vertically upward, or allows the load or chain motor casing to travel vertically downward. The travel of the chain hoist casing or the load vertically up and down is controlled by switches located remotely from the chain hoist casing and coupled to the chain hoist motor by means of an electrical control cable. One or more hooks that are attached to the chain motor casing suspend a load beneath the chain hoist casing. This load is raised and lowered, under the control of the chain hoist operator switches, by the upward and downward travel of the load or the chain hoist along the portion of the chain which is under tension and from which the chain hoist is suspended or by pulling chain in and playing chain out from the casing. One such conventional chain hoist is described in U.S. Pat. No. 2,991,976, while another is described in U.S. Pat. No. 3,960,362.
Chain hoists are utilized extensively and in widely differing applications. They are used in shops, factories, warehouses, shipyards, and numerous other types of commercial and industrial establishments. In many applications of commercially available chain hoists the position of the chain hoist motor and casing relative to the length of the suspended chain upon which it travels or the position of the chain which travels relative to it may be controlled merely by observing either the chain hoist itself, or the load suspended from it. Adjustments to the vertical position of the chain or chain hoist may be performed merely by providing manual inputs to the chain hoist control switches. Indeed, a simply manually operated control is sufficiently accurate for many, many chain hoist applications that do not require precise position control.
On the other hand, there are some applications in which precision control of the chain hoist is required. In the theatrical industry stage sets and props are often moved vertically utilizing general purpose chain hoists, but this movement must be controlled with great precision. For example, different portions of a stage prop may be moved vertically relative to the stage and relative to each other in a closely controlled and intricate sequence and at precise speeds in order to produce special theatrical effects. Precision control of general purpose chain hoists is often necessary in other applications as well. For example, precision control of a general purpose chain hoist may likewise be required at trade shows and expositions in order to create special effects or in order to move interdependent loads in a complex manner. Where precision control of a chain hoist is necessary, visual observation and corresponding adjustment utilizing manual controls is very inadequate and unacceptable.
To provide the necessary precision control for specific applications of general purpose chain hoists, various position-encoding systems have been devised. However, all of these prior position-encoding systems have involved modifications to the chain hoist within the structure of the chain hoist casing. For example, some conventional position-encoding systems for chain hoists have involved the installation of an optical or magnetic encoder within the casing of the chain hoist to sense the rotation of the chain hoist motor or the gear that engages the chain and which is driven by the chain hoist motor within the casing. The internally installed encoder provides corresponding electrical position output signals.
While such conventional position-encoding systems do provide the required positional information, they have significant disadvantages. For one thing, they can be installed within a chain hoist casing only by a person who has extensive knowledge of the internal operations of the components of a chain hoist. The services of such individuals are expensive and often are not readily available.
A further significant disadvantage of such conventional chain hoist encoder systems is that once the chain hoist casing is opened, the manufacturer's warranty for the chain hoist is voided. This is only reasonable since if a person without sufficient expertise attempts to install a position encoder within the casing of a chain hoist, connections can easily be made or broken that will cause permanent damage to the chain hoist and cause it to malfunction. Moreover, tampering with the internally protected components of a chain hoist by persons lacking sufficient expertise can result in alterations to the chain hoist that can cause vary hazardous malfunctions. This can lead to significant property damage and personal injury when the chain hoist is thereafter operated.